Effects of a CO₂-enriched atmosphere on the growth and competitive interaction of a C₃ and a C₄ grass

Summary

Festuca elatior L., C₃, and Sorghum halepense (L.) Persoon, C₄, were grown in mixed and unmixed cultures under 350 and 600 ppm CO₂ for 112 days. High CO₂ levels stimulated increases of total dry weight and leaf surface area in Festuca despite unfavorably high temperatures. In Sorghum, delay of leaf senescence and of floral initiation was attributed to high CO₂ concentrations. Growth of unmixed cultures of Sorghum under 600 ppm CO₂ was relatively poor because of an apparent interaction of high CO₂ with self-shading. All instances of culturexCO₂ interactions are offered in supported of the hypothesis that elevated CO₂ levels will effect the competitive interaction of C₃ and C₄ species. Peak net assimilation rates of C₃ and C₄ plants were seasonally separated at 350 ppm CO₂ but coincided at 600 ppm. Based on our observations of Festuca and Sorghum, we project that global CO₂ enrichment may alter competitive balance between C₃ and C₄ plants and subsequently affect seasonal niche separation, species distribution patterns, and net primary production within mixed communities.